1. Field of the Invention
This invention relates to a method of manufacturing a semiconductor device and, in particular, to a method of forming a low temperature, low viscosity, fluorinated borophosphosilicate glass (FBPSG) layer on the device.
2. Description of Related Art
In the manufacture of semiconductor electronic components, it is necessary to encapsulate the component in a glass or to use glass as an interlayer dielectric film. Typically, the glass layer is a SiO.sub.2 layer which is formed on the surface of the component using chemical vapor deposition (CVD). As a result of increasing demands in industry, the need for finer circuitry patterns and increased circuit density have made it necessary to develop improved glass layers for layering the semiconductor surfaces during the fabrication process. Advanced semiconductor devices, such as highly dense dynamic random access memories (DRAMs) or logic chips, impose severe restrictions on the times, temperatures, and atmospheres of all thermal process steps.
Glass films such as borophosphosilicate glass (BPSG) films or layers, are important in planarizing advanced DRAM devices having increased gate stack heights and integrated circuit densities. Such doped oxide glass layers lower the melting temperature of the glass layer and permit the layers to soften and reflow thereby creating a planar surface on the semiconductor device. The BPSG layers are typically reflowed after deposition in the range of its glass transition temperature which is about 800-850.degree. C. The glass transition temperature is the temperature at which the deposited glass starts to flow. The glass transition temperature is primarily a function of the boron and phosphorous concentrations of the BPSG and depend on the deposition process as well.
It is highly desirable that the reflow temperature be as low as possible for process effectiveness and to avoid temperature damaging effects to the semiconductor device during the fabrication process. As the circuit density and the need for finer circuit patterns have increased, there is a recognized need to formulate and process oxide glass films to fill even smaller gaps on the surface of the semiconductor device without voids or bubbles within the oxide glass layer or surface defects. Up until now, a BPSG layer used as an inter-level dielectric layer can provide void-free fill of structures only as narrow as 0.10 .mu.m with aspect ratios up to 6:1.
However, in DRAM and logic chips having increased gate stack heights and integrated circuit densities, there is a greater need to provide void-free fill of gaps with aspect ratios of greater than 6:1 and at temperatures lower than 750.degree. C. to avoid destroying the chip. Thus, in lowering the thermal budget for DRAM and logic chips, it is highly desirable that the viscosity of the BPSG film be even lower during the fabrication process to provide a void-free fill of structures having aspect ratios greater than 6:1. The viscosity of the BPSG can be decreased by increasing the reflow temperature, which is undesirable, or by increasing the dopant concentrations of boron and phosphorus in the BPSG. In addition, the size of the as-deposited void (i.e., before annealing to reflow the film and reduce or eliminate the void) should be as small as possible. As the aspect ratio of narrow features increase and allowable thermal budgets decrease, minimizing the size of the as-deposited void takes on greater importance.
It is known in the art that fluorine doping of the BPSG increases the surface tension and decreases the viscosity to enhance fill characteristics at lower temperatures but only in high aspect ratio gaps of up to 6:1. However, the dopant concentrations for boron and phosphorus are limited to about 5 weight percent each since exceeding this concentration results in surface crystal growth of boric acid or boric phosphate after deposition. Surface crystals are not desirable due to fabrication integration problems with subsequent lithography, reactive ion etching and chemical mechanical polishing processes. Furthermore, increasing dopant concentrations lead to hygroscopic films.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a method for forming a fluorinated borophosphosilicate glass on a substrate such as a semiconductor wafer having improved as-deposited gap fill properties and a lower reflow temperature without formation of crystallite defects.
It is another object of the present invention to provide a method of manufacturing a semiconductor wafer having a layer of fluorinated borophosphosilicate glass thereon which glass has improved gap fill properties and a lower reflow temperature.
A further object of the invention is to provide a method of forming a borophosphosilicate glass with enhanced gap fill capability to provide a void free fill of structures with aspect ratios greater than 6:1.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.